Trigger assembly

ABSTRACT

A trigger assembly, for use with a power tool having an electric motor, includes a trigger, a conductor coupled for movement with the trigger, and a printed circuit board. The printed circuit board has an inductive sensor thereon responsive to relative movement between the conductor and the inductive sensor caused by movement of the trigger. An output of the inductive sensor is used to activate the electric motor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 15/714,220, filedSep. 25, 2017, now U.S. Pat. No. 10,491,211, which claims priority toU.S. Provisional Patent Application No. 62/400,707 filed on Sep. 28,2016, the entire content of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to power tools, and more particularly totrigger assemblies for power tools.

BACKGROUND OF THE INVENTION

Power tools have triggers that allow operators to activate the workingelement of the power tool when the working element is applied to anobject. Depending on the type of power tool, triggers may be used torotate, extend, retract, oscillate, reciprocate, speed up, and slow downthe working element. Some triggers may allow an operator to cause theworking element to perform more than one of these functions at the sametime. Power tools may also include multiple triggers that are separatelydedicated to these different functions.

SUMMARY OF THE INVENTION

The present invention provides, in one aspect, a trigger assembly foruse with a power tool having an electric motor. The trigger assemblyincludes a trigger, a conductor coupled for movement with the trigger,and a printed circuit board. The printed circuit board has an inductivesensor thereon responsive to relative movement between the conductor andthe inductive sensor caused by movement of the trigger. An output of theinductive sensor is used to activate the electric motor.

The present invention provides, in another aspect, a power tool havingan electric motor, a controller in electrical communication with themotor to activate and deactivate the motor, a trigger, a conductorcoupled for movement with the trigger, and a printed circuit board. Theprinted circuit board has an inductive sensor thereon responsive torelative movement between the conductor and the inductive sensor causedby movement of the trigger. An output of the inductive sensor isdetected by the controller, which in response activates or deactivatesthe electric motor.

The present invention provides, in yet another aspect, a method ofoperating a power tool. The method includes pressing a trigger in afirst direction, moving a conductor over an inductive sensor, outputtinga signal from the inductive sensor, and activating an electric motorbased on the signal.

Other features and aspects of the invention will become apparent byconsideration of the following detailed description and accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a power tool in which a trigger assemblyof the invention may be incorporated.

FIG. 2 is a plan view of a trigger assembly in accordance with anembodiment of the invention, with a trigger shown in a neutral position.

FIG. 3 is a plan view of the trigger assembly of FIG. 2 , illustratingthe trigger rotating in a clockwise direction over a first inductivesensor.

FIG. 4 is a plan view of the trigger assembly of FIG. 2 , illustratingthe trigger rotating in a counter-clockwise direction over a secondinductive sensor.

FIG. 5 is a plan view of an alternate configuration of the firstinductive sensor shown in FIGS. 2-4 .

FIG. 6 is a plan view of an alternate configuration of the secondinductive sensor shown in FIG. 2-4 .

FIG. 7 is a plan view of a trigger assembly, with portions removed forclarity, in accordance with another embodiment of the invention.

FIG. 8 is a plan view of a trigger assembly in accordance with yetanother embodiment of the invention.

FIG. 9 is a flow diagram showing the electrical communication betweenthe first and second inductive sensors of the trigger assembly, areference clock, a sensor unit, and a motor control unit on a printedcircuit board.

Before any embodiments of the invention are explained in detail, it isto be understood that the invention is not limited in its application tothe details of construction and the arrangement of components set forthin the following description or illustrated in the following drawings.The invention is capable of other embodiments and of being practiced orof being carried out in various ways. Also, it is to be understood thatthe phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting.

DETAILED DESCRIPTION

FIG. 1 illustrates a power tool 10 (e.g., an impact wrench) including ahousing 14, an electric motor (e.g., a brushless electric motor 16; FIG.9 ) disposed within the housing 14, and an output shaft which, eitherdirectly or indirectly, performs work on a workpiece during operation ofthe tool 10. In the illustrated embodiment, the output shaft isconfigured as an anvil 18 having a square drive for attachment to acorresponding size socket. However, the output shaft may include adifferent configuration or may include a conventional chuck for receiptof any of a number of different tool bits. Furthermore, the power tool10 may be configured as a non-impact rotary tool (e.g., a drill orscrewdriver) or a non-rotary power tool.

With reference to FIG. 2 , the power tool 10 also includes a triggerassembly 22 for activating and deactivating the motor 16. The triggerassembly 22 includes a trigger 26 pivotably coupled to the housing 14 bya pivot 30, first and second conductors 34, 38 (e.g., pieces of ferrousor non-ferrous metal) supported by the trigger 26 on opposite sides ofthe pivot 30, and a torsion spring 40 for biasing the trigger 26 towarda neutral or “home” position (shown in FIG. 2 ). The trigger assembly 22also includes a printed circuit board (“PCB”) 42 having thereon firstand second inductive sensors 46, 50, which are also components of acontrol system 54 shown in FIG. 9 . The PCB 42 is positioned in closeproximity to the trigger 26 in a grip portion 58 of the housing 14 (FIG.1 ). A power source, such as a battery 62, provides power to the PCB 42and the motor 16 when activated by the trigger assembly 22.

With reference to FIG. 2 , the first and second inductive sensors 46, 50are configured as coil traces on the PCB 42. When an AC voltage isapplied to each of the sensors, 46, 50, an electromagnetic field iscreated. Based on Faraday's Law of Induction, a voltage will be inducedin the conductors 34, 38 in response to relative movement between theconductors 34, 38 and the magnetic fields of the respective inductivesensors 46, 50 which, in turn, produces Eddy currents in the conductors34, 38 that oppose the electromagnetic fields created by the respectiveinductive sensors 46, 50. This changes the inductance of the inductivesensors 46, 50, which can be measured and used as an indicator of thepresence or physical proximity of the conductors 34, 38 relative to thesensors 46, 50. Although not schematically illustrated in FIG. 9 , eachof the inductive sensors 46, 50 is configured as an LC tank circuit, thefrequency of which (hereinafter, the “sensor frequency”) changes inresponse to a change in inductance.

As shown in FIG. 2 , each of the inductive sensors 46, 50 is elongatedand has a uniform number or density of windings throughout the length ofthe sensors 46, 50 between a proximal end 66 and a distal end 70 of eachof the sensors 46, 50. In this embodiment of the trigger assembly 22,the measured change in inductance of the sensors 46, 50 in response tomovement of the conductors 34, 38 relative to the sensors 46, 50 can beused to activate the motor 16 for rotation at a constant speed in eithera forward or reverse direction, depending upon which direction thetrigger 26 is pivoted.

As shown in FIG. 9 , the control system 54 also includes a referenceclock 74, which is also configured as an LC tank circuit. However, thereference clock 74 is isolated from the conductors 34, 38 and thereforeis operable to output a constant reference frequency, the purpose ofwhich is described in detail below. The control system 54 also includesa sensor unit 78, which receives the output of the inductive sensors 46,50 and the reference clock 74, and a motor control unit (“MCU”) 82electrically coupled to the motor 16. The sensor unit 78 continuouslyreceives a first frequency signal 86 indicative of the sensor frequencyof the first inductive sensor 46, a second frequency signal 90indicative of the sensor frequency of the second inductive sensor 50,and a reference frequency signal 94 indicative of the referencefrequency of the reference clock 74.

Using the sensor frequency signals 86, 90 and the reference frequencysignal 94 as inputs, the sensor unit 78 is operable to calculate afrequency ratio, which is a ratio of the sensor frequency to thereference frequency. Specifically, the sensor unit 78 calculates a firstfrequency ratio and a second frequency ratio, and digitally outputs afirst ratio signal 98 indicative of the first frequency ratio and asecond ratio signal 102 indicative of the second frequency ratio to theMCU 82. The MCU 82 is operable to interpolate the first and second ratiosignals 98, 102 to determine whether the trigger 26 has been depressedand in which direction (e.g., clockwise about the pivot 30 orcounter-clockwise). Specifically, if the first ratio signal 98 deviatesfrom an expected initial value (e.g., a ratio of 1:1) while the secondratio signal 102 remains unchanged, the MCU 82 associates this situationwith the trigger 26 being pivoted in a clockwise direction from theneutral position shown in FIG. 2 toward the position shown in FIG. 3 ,coinciding with the first conductor 34 moving over the first inductivesensor 46. Furthermore, the MCU 82 associates pivoting the trigger 26 ina clockwise direction with activating the motor 16 in a forwarddirection at a constant and predetermined speed. Likewise, if the secondratio signal 102 deviates from an expected initial value (e.g., a ratioof 1:1) while the first ratio signal 98 remains unchanged, the MCU 82associates this situation with the trigger 26 being pivoted in acounter-clockwise direction from the neutral position shown in FIG. 2toward the position shown in FIG. 4 , coinciding with the secondconductor 38 moving over the second inductive sensor 50. Furthermore,the MCU 82 associates pivoting the trigger 26 in a counter-clockwisedirection with activating the motor 16 in a reverse direction at aconstant and predetermined speed.

In operation of the power tool 10 using the embodiment of the triggerassembly 22 shown in FIGS. 2-4 , to activate the motor 16 in a forwarddirection, the operator pivots the trigger 26 from the neutral positionshown in FIG. 2 to the position shown in FIG. 3 , causing the firstconductor 34 to move over the first inductive sensor 46. This changesthe inductance of the first inductive sensor 46, which in turn alsocauses the sensor frequency of the first inductive sensor 46 to change.As described above, this change is detected by the MCU 82, which thenactivates the motor 16 in a forward direction at a constant speed. Whenthe operator releases the trigger, it is returned to the neutralposition shown in FIG. 2 by the torsion spring, again causing the firstconductor 34 to move over the first inductive sensor 46. This actionagain causes a change in the sensor frequency of the first inductivesensor 46, which is interpolated by the MCU 82 (as a result of the firstratio signal 98 deviating from an initial value) as the trigger 26returning to the neutral position. Thereafter, the MCU 82 deactivatesthe motor 16, thus stopping forward rotation of the anvil 18.

Likewise, to activate the motor 16 in a reverse direction, the operatorpivots the trigger 26 from the neutral position shown in FIG. 2 to theposition shown in FIG. 4 , causing the second conductor 38 to move overthe second inductive sensor 50. This changes the inductance of thesecond inductive sensor 50, which in turn also causes the sensorfrequency of the second inductive sensor 50 to change. As describedabove, this change is detected by the MCU 82, which then activates themotor 16 in a reverse direction at a constant speed. When the operatorreleases the trigger 26, it is returned to the neutral position shown inFIG. 2 by the torsion spring, again causing the second conductor 38 tomove over the second inductive sensor 50. This action again causes achange in the sensor frequency of the second inductive sensor 50, whichis interpolated by the MCU 82 (as a result of the second ratio signal102 deviating from an initial value) as the trigger 26 returning to theneutral position. Thereafter, the MCU 82 deactivates the motor 16, thusstopping reverse rotation of the anvil 18.

In another embodiment of the trigger assembly (with like features beingidentified with like reference numerals), the uniform inductive sensors46, 50 shown in FIGS. 2-4 may be replaced with inductive sensors 146,150 having a non-uniform winding density along the length of theinductive sensors 146, 150 (FIGS. 5 and 6 ). In other words, each of theinductive sensors 146, 150 includes a relatively low winding density ata proximal end 166 of the sensors 146, 150 (i.e., an end closest to therespective conductors 34, 38 when the trigger 26 is in the neutralposition) and a relatively high winding density at a distal end 170 ofthe sensors 146, 150 (i.e., an end farthest from the respectiveconductors 34, 38 when the trigger 26 is in the neutral position). Inthis embodiment of the trigger assembly, the MCU 82 is also operable tocontrol the speed at which the motor 16 operates in proportion to thedegree to which the trigger 26 is pivoted.

In operation of the power tool 10 using the embodiment of the triggerassembly with the inductive sensors 146, 150 of FIGS. 5 and 6 , toactivate the motor 16 in a forward direction, the operator pivots thetrigger 26 from the neutral position shown in FIG. 2 in a clockwisedirection, causing the first conductor 34 to move over the firstinductive sensor 146. This changes the inductance of the first inductivesensor 146, which in turn also causes the sensor frequency of the firstinductive sensor 146 to change. However, rather than the first ratiosignal changing between an expected initial value (e.g., 1:1) and analternate value (e.g., one greater than or less than 1:1) as is the casewhen using the inductive sensors 46, 50 of FIG. 2 having a uniformwinding density, the first ratio signal input 98 to the MCU 82continuously changes from the initial value (e.g., 1:1) to a final(e.g., a maximum or minimum) value coinciding with placement of thefirst conductor 34 above the distal end 170 of the first inductivesensor 146. This change is detected by the MCU 82 which, depending uponthe degree to which the trigger 26 is pivoted in the clockwisedirection, activates the motor 16 in a forward direction at a rotationalspeed that is proportional to the degree to which the trigger 26 ispivoted.

If the trigger 26 is pivoted to an intermediate position and then heldstationary, the MCU 82 will continue to drive the motor 16 at a constantrotational speed proportional to the degree to which the trigger 26 isinitially pivoted, until the trigger 26 is either depressed to pivot thetrigger 26 further in a clockwise direction (to thereby accelerate themotor 16 to a higher speed) or released to deactivate the motor 16. Ifthe trigger 26 is further pivoted in the clockwise direction, the firstconductor 34 is moved further along the length of the first inductivesensor 146, closer to the distal end 170 of the first inductive sensor146. This action again causes a change in the sensor frequency of thefirst inductive sensor 146, with the magnitude of the first ratio signal98 moving further from the initial value (e.g., 1:1) and toward thefinal (e.g., a maximum or minimum) value, prompting the MCU 82 toaccelerate the motor 16 to a rotational speed proportional with thedegree to which the trigger 26 is pivoted in the clockwise direction.The MCU 82 is also operable to drive the motor 16 at a variablerotational speed as described above, but in a reverse direction, inresponse to the trigger 26 being pivoted in a counter-clockwisedirection from the neutral position shown in FIG. 2 .

FIG. 7 illustrates a trigger assembly in accordance with anotherembodiment of the invention, with like features being shown with likereference numerals. The trigger assembly is similar to that describedabove using the inductive sensors 146, 150 shown in FIGS. 5 and 6 , butthe second conductor 38 and the second inductive sensor 150 are omitted.And, in the neutral position of the trigger 26, the first conductor 34is located approximately between the proximal and distal ends 166, 170of the first (and only) inductive sensor 146.

In this embodiment, the MCU 82 is programmed to activate and drive themotor 16 in a forward direction at a rotational speed proportional tothe degree to which the trigger 26 is pivoted in a clockwise directionfrom the neutral position, which further displaces the first conductor34 toward the distal end 170 of the first inductive sensor 146.Likewise, the MCU 82 is programmed to activate and drive the motor 16 ina reverse direction at a rotational speed proportional to the degree towhich the trigger 26 is pivoted in a counter-clockwise direction fromthe neutral position, which further displaces the first conductor 34toward the proximal end 166 of the first inductive sensor 146. When theoperator releases the trigger 26, it is returned to its neutral positionby the torsion spring, again causing the first conductor 34 to move overthe first inductive sensor 146. This action again causes a change in thesensor frequency of the first inductive sensor 146, which isinterpolated by the MCU 82 as the trigger returning to the neutralposition (coinciding with placement of the first conductor 34approximately between the proximal and distal ends 166, 170 of the firstinductive sensor 146). Thereafter, the MCU 82 deactivates the motor 16,thus stopping rotation of the anvil 18.

A trigger assembly 322 in accordance with yet another embodiment of theinvention is shown in FIG. 8 . In this embodiment, a slidable trigger326 supporting a conductor 334 thereon is employed. The slidable trigger326 is biased by a spring to a neutral position spaced from a single,linear inductive sensor 346 having a non-uniform winding density. Inthis embodiment, a separate direction switch (not shown) on the housing14 of the power tool 10 is employed to toggle rotation of the motor 16between forward and reverse directions. In the same manner as describedabove, the MCU 82 is programmed to increase the rotational speed of themotor 16 as the slidable trigger 326 slides over the inductive sensor346 as the conductor 334 approaches the distal end 370 of the inductivesensor 346. Likewise, the MCU 82 is programmed to decrease therotational speed of the motor 16 as the slidable trigger 326 slides overthe inductive sensor 346 in an opposite direction as the conductor 334approaches the proximal end 366 of the inductive sensor 346. And, theMCU 82 is programmed to hold the rotational speed of the motor 16 at aconstant value if the slidable trigger 326 stops anywhere between theproximal and distal ends 366, 370 of the inductive sensor 346.

The trigger assemblies of FIGS. 2-7 allow the motor 16 to be controlledwithout a secondary direction switch to otherwise toggle the motor 16between forward and reverse rotational directions, thus reducing thenumber of components required to manufacture the tool 10 and theattendant cost. Also, because the inductive sensors 46, 50, 146, 150,346 function as non-contact switches, the trigger assemblies 22, 322disclosed herein are expected to have greater longevity than atraditional contact-based trigger switch, which can wear over time.

Various features of the invention are set forth in the following claims.

What is claimed is:
 1. A power tool comprising: an electric motor; acontroller in electrical communication with the motor to activate anddeactivate the motor; a trigger; a conductor coupled for movement withthe trigger; a printed circuit board having an inductive sensor thereonresponsive to relative movement between the conductor and the inductivesensor caused by movement of the trigger, wherein an output of theinductive sensor is detected by the controller, which in responseactivates or deactivates the electric motor; a sensor unit incommunication with the controller; and a reference clock configured toprovide a reference frequency signal to the sensor unit that isindicative of a reference frequency of the reference clock, wherein theoutput of the inductive sensor is a sensor frequency signal indicativeof a sensor frequency of the inductive sensor, wherein the sensorfrequency of the inductive sensor is configured to change based onrelative movement between the conductor and the inductive sensor,wherein the sensor unit is configured to receive the sensor frequencysignal from the inductive sensor and output a ratio signal to thecontroller, which is a ratio of the sensor frequency to the referencefrequency, and wherein the controller activates or deactivates the motorbased upon the ratio signal.
 2. The power tool of claim 1, wherein theinductive sensor is first inductive sensor, the conductor is a firstconductor, and the output is a first output, and wherein the power toolfurther comprises a second conductor coupled for movement with thetrigger, and a second inductive sensor on the printed circuit boardresponsive to relative movement between the second conductor and thesecond inductive sensor caused by movement of the trigger, wherein asecond output of the second inductive sensor is detected by thecontroller, which in response activates the electric motor.
 3. The powertool of claim 2, wherein the first output of the first inductive sensoris detected by the controller, which in response activates the electricmotor in a first rotational direction, and wherein the second output ofthe second inductive sensor is detected by the controller, which inresponse activates the electric motor in a second rotational directionthat is different than the first rotational direction.
 4. The power toolof claim 1, wherein the inductive sensor is a coil trace having aproximal end located proximate the trigger and a distal end, and whereinthe distal end has a different winding density than the proximal end. 5.The power tool of claim 4, wherein, in response to the conductor movingaway from the proximal end of the inductive sensor and towards thedistal end, a rotational speed of the motor is accelerated by thecontroller, and wherein, in response to the conductor moving away fromthe distal end of the inductive sensor and towards the proximal end, therotational speed of the motor is decelerated by the controller.
 6. Thepower tool of claim 5, further comprising a spring biasing the triggertoward a neutral position in which the conductor is closer to theproximal end than the distal end.
 7. The power tool of claim 6, whereinthe conductor is a first conductor, the coil trace is a first coiltrace, and the output is a first output detected by the controller toactivate the motor in a first rotational direction, and wherein thepower tool further comprises a second conductor coupled for movementwith the trigger, and a second inductive sensor configured as a secondcoil trace on the printed circuit board having a proximal end locatedproximate the trigger and a distal end, wherein the distal end of thesecond coil trace has a different winding density than the proximal endof the second coil trace, wherein the second inductive sensor isresponsive to relative movement between the second conductor and thesecond inductive sensor caused by movement of the trigger, and wherein asecond output of the second inductive sensor is detected by thecontroller, which in response activates the motor in a second rotationaldirection that is different than the first rotational direction,wherein, in response to the second conductor moving away from theproximal end of the second coil trace and towards the distal end of thesecond coil trace, a rotational speed of the electric motor isaccelerated by the controller, and wherein in response to the secondconductor moving away from the distal end of the second coil trace andtowards the proximal end of the second coil trace, the rotational speedof the motor is decelerated by the controller.
 8. The power tool ofclaim 1, wherein the inductive sensor is a coil trace having a first endand a second end that has a different coil density than the first end,and wherein the power tool further comprises a spring biasing thetrigger to a position in which the conductor is located in a neutralposition between the first end and the second end, wherein, in responseto the conductor moving away from the neutral position and towards thefirst end of the coil trace, the output of the inductive sensor isdetected by the controller, which in response activates the motor in afirst rotational direction and accelerates a rotational speed of themotor, and wherein, in response to the conductor moving away from theneutral position and towards the second end of the coil trace, theoutput of the inductive sensor is detected by the controller, which inresponse activates the motor in an opposite, second rotational directionand accelerates the rotational speed of the motor.
 9. The power tool ofclaim 1, wherein the controller is configured to activate the motor inone of a first rotational direction or an opposite, second rotationaldirection in response to a change in the first ratio signal.
 10. Thepower tool of claim 1, wherein a parameter of the motor is controlled inproportion to the movement of the trigger using the output of theinductive sensor.
 11. The power tool of claim 1, wherein the conductormoves between a first position and a second position, wherein the firstposition is outside the detection area of the inductive sensor and thesecond position is within the detection area of the inductive sensor.12. A method of operating a power tool, the method comprising: pressinga trigger in a first direction; moving a conductor over an inductivesensor; outputting a sensor frequency signal from the inductive sensorindicative of a sensor frequency of the inductive sensor, wherein thesensor frequency of the inductive sensor is configured to change basedon relative movement between the conductor and the inductive sensor;activating, using a controller of the power tool, an electric motorbased on the signal; receiving a reference frequency signal indicativeof a reference frequency of a reference clock; and receiving the sensorfrequency signal from the inductive sensor and outputting a ratio signalto the controller, which is a ratio of the sensor frequency to thereference frequency, and wherein the motor is activated or deactivatedbased upon the ratio signal.
 13. The method of claim 12, wherein theinductive sensor is a coil trace having a proximal end located proximatethe trigger and a distal end, and wherein the distal end has a differentwinding density than the proximal end, and wherein the method furthercomprises: moving the conductor away from the proximal end of theinductive sensor and towards the distal end of the inductive sensor; andaccelerating the rotational speed of the motor as the conductor is movedfrom the proximal end of the inductive sensor towards the distal end.14. The method of claim 13, further comprising: releasing the trigger;biasing the trigger in a second direction that is opposite the firstdirection; moving the conductor away from the distal end of theinductive sensor and towards the proximal end of the inductive sensor;and decelerating the rotational speed of the motor as the conductor ismoved from the distal end of the inductive sensor to towards theproximal end.
 15. The method of claim 12, wherein activating theelectric motor comprises activating the electric motor in a firstrotational direction.
 16. The method of claim 15, wherein pressing thetrigger in the first direction comprises pivoting the trigger in a firstpivotal direction, wherein the conductor is a first conductor and theinductive sensor is a first inductive sensor, and wherein the methodfurther comprises: pivoting the trigger in a second pivotal directionthat is opposite the first pivotal direction; moving a second conductorover a second inductive sensor; outputting a second signal from thesecond inductive sensor; and activating the electric motor in a secondrotational direction that is different than the first rotationaldirection based on the second signal.
 17. The method of claim 12,further comprising controlling the motor in proportion to the movementof the trigger using the output of the inductive sensor.
 18. The methodof claim 12, further comprising moving the conductor between a firstposition and a second position, wherein the first position is outsidethe detection area of the inductive sensor and the second position iswithin the detection area of the inductive sensor.
 19. The method ofclaim 12, wherein the motor is activated in one of a first rotationaldirection or an opposite, second rotational direction in response to achange in the first ratio signal.